Method of preventing depositions of pitch from sulphite pulp



April 12, 1960 Filed June 13, 1955 s. P. H. E. HOLGERSSON ETAL 2,932,602

METHOD OF PREVENTING DEPOSITIONS OF PITCH FROM SULPHITE PULP 5 Sheets-Sheet 1 Fig.1

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April 1960 s. P. H. E. HOLGERSSON ETAL 2,932,502

METHOD OF PREVENTING nzposrrxous 0F PITCH FROM SULPHITE PULP Filed June 13, 1955 3 Sheets-Sheet 2 Fig.3

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A ril 12, 1960 s. P. H. E. HOLGERSSON ETAL 2,

METHOD OF PREVENTING DEPOSITIONS OF PITCH FROM SULPHITE PULP Filed June 13, 1955 3 Sheets-Sheet. 3

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United States Patent METHOD OF PREVENTING DEPOSITIONS 0F PITCH FROM SULPHITE PULP Sigbjiirn PaulHerbert Ebbinghaus Holgersson, Ockelbo,

and Kjell Johan Ingemar Groth, Lidingo, Sweden, assignors to Kopparfors Aktiebolag, Ockelbo, Sweden, a corporation of Sweden Application June 13, 1955, Serial No. 515,192 Claims priority, application Sweden June 18, 1954 3 Claims. (Cl. 162--158) The invention relates to improvements in a method of preventing depositions of pitch from sulphite pulp, particularly suspensions. of. such pulp.

Sulphitc pulp, even the bleached quality, contains almost without exception finely dispersed particles of pitch adhering to the fibres. At times this pitch causes considerable trouble in the wet machine as well as in the subsequent manufacture of'paper or carton. Insofar as the pitch particles are sticky they clog together and deposit on beater members, press rolls, wet felts etc. As a consequence, the operation must often be stopped for cleaning. Further, clogged particles of pitch often cause spots on the surface of the paper, In modern, fast-running paper machines, the presence of sticky pitch makes it impossible to maintain the speed of the machine, so that a loss of capacity cannot be avoided.

The stickiness of the pitch and its tendency to clog is considered todepend on its consistence in such a way that a softer pitch often causes troubles, while harder pitchis harmless. The consistence, in turn, depends on the proportion of unsaturated, organic compounds contained in the pitch. Such compounds can be oxidized by the oxygen of the: air and thuswholly or partly cohverted'l into oxyor hydroxycompounds having; a higher meltingpoint and a harder, more harmless consistence; To obtain such an oxidation it is necessary to store the i surface active agents are added to the pulp in such minor amounts that the pitch particles are fixed to the fibres of the pulp. As a matter of fact, investigations have shown that such a very effective fixation can be obtained, provided the added amounts of the agents in question are kept'lvery low; An increased addition of said agents causes the pitch particles to be instead released overt to a greater extent than in pulp not treated at all, and a further increase of the amount of agents results in a more or less complete dispersion or emulsification of the pitch. The explanation of this result will probably'beasj follows'z i 7 Generally, pitch" contains a mixture of neutral hydracarbons and compounds containing anionic carbonyl groups having a hydrophilic part. To a. certain extent 7 such carboxyl groups are concentrated to the surfaces of Woodfor a very long period of time, such as l4 20 months, so'that'. the pitch hastimeto agez Also asulphite pulp containing. sti'cky' pitch can be made quite usefuliby a long time" of storage. However, in both cases ilargestorag'e-spaces are occupied and the large'stocks: re- :quire: a :large capital. investment. Besides, the method does not: always give the desired result, inthat sometimes not even a" considerably prolonged period 'of storage: for the'wood or pulp is suflicient to eliminate "the stickinessofthespitcli. Another drawback of along time of storage is that the wood is damaged byblue-stain rfungus orrot, which means not only adeterioration of ithe'quality ofJthe finaliproduct but also a loss of wood, .in many cases amountingto asinuclr as 5%. Thus, considerable economical advantages woul'd be obtained, if

fi'eshz wood could be used for the pulp production, in that the planning of. the felling. would be simplified and the necessity of keepinggreat-amountsof wood and pulp sin storage would beteliminated.

It haspreviously. beenzproposed to reduce the-troubles of: sticly'pitcharising in connection with sulphite pulpby :adding; to a fibre suspension diiferent surface active agents iinamounts: sufficient to disperseoremulsify the pitch:in v therwater-phase-ofthe-suspension. However, the method has no such tangible: effect that thetroubles arewholly eliminated. Moreover, it may occur, when dilutingthe suspcnsiom. that the e'mulsion is broken and the dispersed particles. are again precipitated. Further, rather great Eamounts of emulsifying; agent arerequired; which intgvolves' appreciable extracosts;-

which troubles of sticky pitch are entirely eliminated.

the pitch particles, whereby the particles are easily clogged and released from the fibres. When adding a cationic, surface active agent its end groups being positively charged are attracted by the negative carboxyl groups. .Thus, the pitch is' made hydrophobic and is less influenced bythe water, which results in a. fixation of the pitch particles on the fibres. H The sizeof the pitch surface and the number of carboxyl groups in it determine the required amount of cationic surface active agent. If the addition is increased, the pitchsurface will again become more hydrophilic by attracting, due to Van der Waal forces, an outer layer of long-chained ions in this case turning their hydrophobic hydrocarbon parts inwards to the out-turned hydrocarbon parts of the layer of ions first attracted. This results in a release of the pitch. An ernulsification takes place only whcnafurtlier excess of cationic surface active agent is available.

Among cationic, surface active agents useful in the method according to the invention may bementioned long-chained hydrocarbon compounds having a cationic part containing one or more three-valent or five-valent nitrogen atoms, such as primary, secondary or tertiary alkyl amines, alkyl-ammonium bases and" alkyhpyridine bases as Well as derivatives and salts of tliese compoundsp Among the compounds enumerated the primary amines are most suitable as they show a very good effect. Generally, the amines have a liimted solubility in water but dissolved in suitable solvents or in the form of dispersions in water they will yet to a great extent bring about the intended action on the pitchparticles. However, it is to prefer to use their water soluble salts, such as acetates, sulphates or chlorides.

If a sulphite pulp contains sticky pitch, this fact becomes particularly evident at the treatment in a disintegrator. Owing to the vigorous kneading of the pulp the pitch particles clogland settle on the various parts of the machine. An analytical method fortesting the, presence of sticky pitch is based on this fact'a'nd has here been used to investigate the effect of' the method according to the invention when using some different cationic surface active agents; Pieces of a dry sheet of cellulose were weighed and then moistenedwith a measured amountof a solution-of a cationic surface active agent; Th'e pieces' thus treated were again dried and theh-- defibra'te'diii a measured quantity of water in a glass beaker. The fibre suspension, adjusted to the desired concentration, was subjected to a vigorous agitation during two hours by means of a submerged copper propeller which was caused to rotate at a speed of about 1000 rpm; Duringi'this rotation the propeller was-coated-by a -ve'ry thin layer of pitch. The propeller was weighed dry before and after the test. It is self-evident that the numerical values ob- V tained by such a method are not directly applicable in practice, but in any case the results would clearly show the tendency when adding varying amounts of agents.

In the following Examples 1-4 the method was applied on unbleached sulphite pulp produced from spruce wood which had been stored for only two months and still contained a considerable amount of sticky pitch. The temperatures were all the time kept at 20 C. and the pH at 7.0.

Example 1 Amount of BF added Pitch deposition mg. per g. mg. per 1. in mg.

dry base suspension The values in the table are inserted in a graph shown in Fig. l of the accompanying drawings, where the amount of BF is indicated in milligrammes per litre along the abscissa, while the amount of pitch is indicated in milligrammes along the ordinate.

Example 2 The pulp was used in 0.4% concentration. The same cationic agent, BF," as in Example 1.

Amount of "BF added Pitch deposition mg. per g. mg. per 1. in mg.

dry base suspension The values are inserted in the graph in Fig. 2.

Another primary alkyl amine, stearyl amine acetate, was added in series of experiments corresponding to the Examples 1-4 and gave similar results.

Example 3 The pulp was used in 4% concentration. As cationic agent cetyl pyridine chloride was used.

2,932,602 7 r. I, 4 V p Amount of cetyl pyridine chloride added Pitch deposition in mg. mg. per g. mg. per 1.

dry base suspension The values are inserted in the graph in Fig. 3.

Example 4 The pulp was diluted to 0.4% concentration. pyridine chloride as cationic agent.

Cetyl Amount of cetyl pyridine chloride added Pitch deposition in mg. mg. per g. mg. per 1.

dry base suspension The values are inserted in the graph in Fig. 4.

As apparent, the graphs in Figs. 1-4 show fundamental similarities, although the appearance may, of course, vary considerably in dependence on the amount of pitch, the quality of the pitch and the concentration of the fibre suspension. At increased additions of the cationic agent the amount of pitch deposited on the agitating propeller first sinks to a minimum and then increases to a value higher than that for untreated pulp. This result is quite in accordance with the theoretical explanation given above. After having reached a maximum value the amount of pitch deposited sinks again, although rather slowly, owing to the dispersion. Obviously, great amounts of surface active agents would be required to obtain a satisfactory emulsification, and such a method would therefore be uneconomical, irrespective of the inconveniences mentioned above.

It is also apparent from the graphs that the alkyl amine salt has a markedly better eifect in comparison to the quaternary ammonium salt cetyl pyridine chloride, and this has also been confirmed by practical tests in the mill. In fact, the results obtained with alkyl amine salts are to be considered most satisfactory.

When comparing the results obtained with 4% and 0.4% pulp concentration it becomes apparent that the amount of cationic surface active agent should rather be calculated in proportion to the aqueous phase of the fibre suspension than in proportion to the dry pulp. This observation corresponds to previous experiences with regard to surface active substances. Nevertheless itmight in practice in many cases beto prefer to calculate the amount of added agent on dry base, as for instance when the addition is made to a thickened pulp which is then dried and formed into bales or rolls to be delivered to a paper mill. 1

As indicated above, the greatest importance of the new method lies in the possibility of eliminating the difficulties of sticky pitch in the production of paper, i.e. above all in the operation of the paper machines. Here only pulp concentrations below 1% are used, and mostly the concentrations are, only 0.3 to Therefore the, con,-

centration; of 0.41%". used' in certain. tests and the" amounts ofs'urface active, agentsl there, required are of; essential interest.

The addition of the surface active agents may be performed after the digesting at any stage of the manufacture in the, sulphite, mill: or paper mill. To avoid an necessary losses of agents due to the removal of excess qflwlater from the pulp it may, however, be desired. to add said agents at a 'stage'of" the process where either only a small amount of water is removed by a subsequent purification or the water is returned to be used again. Thus, if desired, the addition may take place after the pulp has been thickened to about in a wet machine. In the following a suitable embodiment of the invention will be described with reference to Fig. 5 which diagrammatically illustrates a wet machine in a sulphite mill.

The pulp which has been diluted 'to a desired concentration is supplied from a stuff-chest 1 to an endless, rotating wire 2 in a wet machine. A row of suction boxes 4, a rotating suction belt 5 and a suction couch roll 6 are placed after each other at the underside of the wire part over which the pulp 3 passes. From the wire-cloth the pulp passes through three felt presses 7-9 placed after each other and is then introduced into a drying loft 10. After the rotary belt 5 and before the couch roll 6 the pulp has generally a concentration of about 10%. The content of water is successively reduced during the subsequent suction and pressing so that it amounts to about 50% after the last felt press. The finished pulp sheet discharged from the drying loft has generally a moisture content of about 10%. Of course, machines of this type are well-known and need not be described more in detail.

It has proved especially suitable to add a solution of the surface active agent or agents to the pulp on the wirecloth at some point between the rotary suction belt and the couch roll. The solution is supplied from a storage container through a tube 11 mounted transversely to the machine and provided with a row of nozzles. The jets hit a plate 12 mounted along the tube and directed towards the layer of pulp, so that the liquid is distributed over the upper surface of the pulp in the form of a continuous, thin curtain. The solution penetrates the pulp layer, as liquid flows off from its underside. If the amount of liquid added is approximately equal to the weight of pulp, dry base, it is possible to obtain that the water content (50%) of the pulp after the last felt press is for the greater part derived from the solution supplied, which has now displaced the underlying water layer. In other words, it is possible to determine the amount of solution in such a way that the pulp sheet entering the drying loft is entirely impregnated with the surface active agent, at the same time as no major amounts thereof are lost.

Of course, the amount of surface active agents is so determined that the pulp sheet discharged from the drying loft contains a sufiicient amount thereof to ensure that no pitch troubles arise at the further treatment of the pulp in the paper mill.

The method according to the invention was further tried on unbleached sulphite pulp produced from the worst possible raw material, i.e. fresh spruce wood, which would normally cause considerable troubles of sticky pitch. The addition of the surface active agents was carried out as described above, i.e. to the pulp upon the wire-cloth before the suction couch roll, and samples were taken from the dried pulp discharged from the drying loft. following method:

40 grammes of dry pulp were ground together with 1500 millilitres of water in a ball mill of the type Lampn for minutes. The ground pulp was dis- The samples were tested according to the charged and another 40 grammesofpul'p from the same samplewere supplied together with 1500 millilitresfof' water and ground for 30 minutes. Tensuch grindings were performed in succession, whereupon the deposition of pitch in the mill was extracted by a mixture of ether and alcohol. The solution was evaporated and the remaining pitch was weighed. The quantity. of" pitch gained in this way must preferably not exceed 30 milligrammes, ifthe pulp is to be considered as quite satisfactory with regard to the 'depositionof' pitch. When tes'ting'a sample of untreated pulp, ll0'milli'grammesof pitch were deposited in the mill. Such a pulp would no doubt beuseless in that condition.

The same pulp was used in all the tests and the surface active agents were supplied in water solutions. The results appear from the following examples.

Example 5 When adding the cationic surface active agent stearyl amine acetate in a concentration of 0.1%, calculated on dry pulp, 21 milligrammes of pitch were obtained in the ball mill of Lampn.

Example 6 The alkyl amine acetate called BF used in Examples 1 and 2 was added in an amount of 0.05%, calculated on dry pulp. 20 milligrammes of pitch were obtained.

The results obtained in these examples are very satisfactory, particularly in view of the troublesome raw material. In practice these results mean that no pitch is deposited on the parts of the machine getting into contact with the pulp during its treatment, nor are spots consisting of clogged particles of pitch formed on the surface of the paper. Especially it must be considered as highly surprising that it has now become possible, according to the invention, to use fresh wood without troubles of pitch arising.

As pointed out, the numerical values obtained in the tests may not always be directly applied in practice. In the first place, the required quantities of surface active agents are dependent on the propontion of pitch in the pulp, the nature of the pitch, the concentration of the fibre suspension and the kind of surface active agent used, but also such factors as temperature and pH are of importance. Thus, the amount of surface active agent cannot be calculated in advance but has to be determined in each special case by practical experiments. However, with regard to pulp concentrations used in the paper industry the amount of added agent may generally be kept below 0.1% and seldom exceeds 0.2%, calculated on dry base. In most cases, however, these values are too high, and as an example it may be mentioned that an excellent result was obtained already with 0.01% as appears from Example 2.

A determination of the amount of surface active agent required involves no problem. As mentioned, some of the most important objects of the invention are to prevent deposition of pitch on press rolls and felts in the paper machine as well as formation of spots of pitch on the surface of the paper. If the pulp contains too great or too small an amount of surface active agents, such spots .of'pitch appear immediately on the paper and a layer of sticky pitch has been deposited on the press rolls already after 1-2 hours normal run. A too great addition becomes apparent also by a certain foaming and may be corrected by adding untreated pulp.

What we claim is:

1. A method of preventing depositions of pitch from unbleached sulphite pulp and suspensions of such pulp, which comprises adding to the pulp at least one cationic surface-active agent selected from the group consisting of alkyl amines, alkyl-amrnonium bases, alkyl-pyridine bases and the salts thereof in an amount of at most 0.1%, cal culated on the dry pulp, effective to cause .a fixation of the particles of the pitch on the fibers of the pulp.

'7 a 2. A method of preventing depositions of pitch from unbleached sulphite pulp and suspensions of such pulp, which comprises adding to the pulp a water soluble salt of a primary alkyl amine in an amount of at most 0.1%, calculated on the dry pulp, efi'ective to cause a fixation of the pitch on the fibers of the pulp.

3. A method of preventing depositions of pitch from unbleached sulphite pulp and suspensions of such pulp, which comprises impregnating a supported sheet of partially dehydrated pulp with at least one cationic, surfaceactive agent selected from the group consisting of alkyl amines, alkyl-ammonium bases, alkyl-pyridine bases and the salts thereof in an amount of at most 0.1%, calculated References Cited in the file of this patent UNITED STATES PATENTS Fritz Jan. 24, 1939 Reynolds July 6, 1954 

1. A METHOD OF PREVENTING DEPOSITIONS OF PITCH FROM UNBLEACHED SULPHITE PULP AND SUSPENSIONS OF SUCH PULP, WHICH COMPRISES ADDING TO THE PULP AT LEAST ONE CATIONIC SURFACE-ACTIVE AGENT SELECTED FROM THE GROUP CONSISTING OF ALKYL AMINES, ALKYL-AMMONIUM BASES, ALKYL-PYRIDINE BASES AND THE SALTS THEREOF IN AN AMOUNT OF AT MOST 0.1%, CALCULATED ON THE DRY PULP, EFEFECTIVE TO CAUSE A FIXATION OF THE PARTICLES OF THE PITCH ON THE FIBERS OF THE PULP. 